The present invention is directed to a method for the selective etching of SiO.sub.2 layers, particularly for selective removal of sacrificial layers relative to metallizations.
when etching free micromechanical structures with a sacrificial layer, disadvantages in the prior art are that, the micromechanical structure remains adhering to the surface of the chip after the wet etching fluid has dried and that the etchant used for the etching cannot be used selectively relative to, for example, aluminum. In wet-chemical etching, the liquid etchant is subsequently removed from the surface of the etched chip with what is also a liquid chemical. This chemical is then removed in that it is converted into the gaseous aggregate state, so that the structure that has been etched free does not remain adhering to the surface of the chip. When micromechanical structures are to be realized from, for example, a metal (for example, a metallization of aluminum), then a sacrificial layer of silicon dioxide cannot be selectively removed relative to the metal with the hydrofluoric acid (hydrogen fluoride in aqueous solution), which is usually employed as etchant, because the metal would also be attacked and decomposed by the hydrofluoric acid. Metallizations of aluminum such as, for example, terminal contacts or interconnects must therefore, for example, be protected against the etching attack with complicated measures before the etching with hydrofluoric acid. This can occur, for example, by applying resist masks. In the manufacture of micromehanical structures that are not composed of silicon, materials other than silicon dioxide must therefore be used for sacrificial layers. The employment of etchants other than hydrofluoric acid is very involved and is also not compatible with the standard manufacturing processes. An improved etching process with HF was presented in 1991 by D. Syverson at the Institute of Environmental Sciences as FSI Technical Report 369.